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There were nearly 10,000 new cases of chlamydia diagnosed in Toronto in 2014, the most recent year where complete datasets were available. The infection is easily transmitted and was the most prevalent sexually transmitted infection (STI) across the city.

The increase is due in part to better laboratory testing according to Toronto Public Health. “It is likely that these tests are picking up infections that would not have been detected with earlier generation tests,” said Dr. Rita Shahin, Toronto’s Associate Medical Officer of Health.

She adds that chlamydia is so common because it often remains symptomless, leading to a greater likelihood that those infected will spread the disease to others.

“STI rates in Toronto are high compared to other jurisdictions.”

Gonorrhea is the second most common sexually transmitted infection in the city, and over the years doctors have come across a small number of drug-resistant cases.

The majority of these have been seen in men who have sex with men, and the disease is “generally able to be treated with combinations of antibiotics,” said Dr. Shahin. But health officials in other countries have expressed concerns that drug-resistant gonorrhea could become untreatable.

When looking at the distribution of new cases of STIs across Toronto denser pockets of infection emerge throughout the city’s 140 neighbourhoods. Rates of chlamydia in 2014 were higher in the city’s northwest corner – near Downsview, Jane and Finch and York University – and downtown.

“There is some correlation between higher STI rates and lower socioeconomic status that would help explain the geographic distribution of chlamydia rates,” said Dr. Shahin. One study from the Centers for Disease Control and Prevention found that “lower income is associated with less access to preventative information and healthcare, and increased use of sex as a psychosocial coping mechanism.”

Infection rates of hepatitis B were higher in the Steeles/Milliken area and Kensington – Chinatown. Hepatitis B is a serious liver infection that can increase the risk of organ failure and cancer.

“The higher number of cases in the northeast of the city is likely due to a combination of factors, including immigration and settlement patterns,” said Dr. Shahin. Essentially people are arriving from locations where the virus is more common.

In general there were higher rates of sexually transmitted infections in the Yonge – Church corridor, an area that encloses Toronto’s “gay village.”

STI rates are generally higher among men who are sexually active with other men, but “contrary to popular belief, gay men do not have more sex than others,” said Dr. David Brennan, associate professor at the University of Toronto and Ontario HIV Treatment Network Research Chair in Gay and Bisexual Men’s Health. “Most of the research in this area has shown that they may have slightly more partners over a lifetime but the numbers are so much smaller that they are not statistically significant.”

Rates of STIs are higher in the gay community because the pool of potential partners is much smaller. “Given that estimates of gay people run from two to ten per cent of the population, then when you consider that a gay man might have sex with another gay man, they are part of a smaller pool of people,” said Dr. Brennan. “Once an STI (such as HIV) is introduced into that smaller pool of gay men in the population, then there is a much greater risk that they will come into contact with it.”

In 2014, the rate of new HIV cases was highest in Cabbagetown – South St. James Town. There were 14 new infections within a population of 12,060, which is one in every 861 people. HIV infections overall have fallen across the city from 569 in 2004 to 407 in 2014.

With respect to chlamydia and gonorrhea, officials at Toronto Public Health believe the impact from improved lab testing has likely plateaued, but Dr. Shahin says it’s very difficult to predict whether infection rates will rise or fall.

“There are many factors that affect STI rates including condom use, testing behaviours, number of sexual partners, and increased use of online apps.”

Recently within Toronto’s gay community there has been growing interest in the use of PrEP (Pre Exposure Prophylaxis). “PrEP is the use of Truvada (a drug used to treat HIV) by someone who is HIV-negative,” explained Dr. Brennan. “If they take this medication before possibly being exposed to HIV and then continue to take it afterward, their chances of HIV infection are very low.”

This has led to some abandoning condom use, and Truvada does not protect against other STIs. Officials at Toronto Public Health say because the use of PrEP is still relatively new, there is no data suggesting it is contributing to a rise in other infections; however, one study out of the US did confirm that finding.

“There was a big study out of San Francisco that showed that among guys who were using PrEP, there were spikes in other STIs like syphilis and gonorrhea,” said Dr. Brennan.

To curtail the spread of infection Toronto Public Health has, among other things, engaged in a large social media campaign to promote safe sex and responsible behaviour.

The city has even created its own branded condom, condomTO, meant to “reinvigorate and normalize condom use, and combat sexual shame and stigma,” according to Dr. Shahin.

“The response has been very positive,” she said. Condoms still remain one of the most effective tools to protect against sexually transmitted infections.